Solar powered 24hr timelapse photography

Bought the power management unit and three batteries:

Bought two 2W solar panels, hoping this will give enough output.

And another shot:

Initial test script power.py loaded as a systemd service. This simply saves a datetime line to a file to show the Pi is waking up at midday each day.

Create a file :

/lib/systemd/system/power.service

containing the following (with paths adjusted for your own script location):

    [Unit]
    Description=Runs Timelapse power cycles
    After=multi-user.target

    [Service]
    Type=idle
    ExecStart=/usr/bin/python3 /home/bernard/git/timelapse/power.py

    WorkingDirectory=/home/bernard/git/timelapse
    Restart=on-failure

    # Connects standard output to /dev/null
    StandardOutput=null

    # Connects standard error to journal
    StandardError=journal

    [Install]
    WantedBy=multi-user.target

Then set permissions of the file

sudo chown root:root /lib/systemd/system/power.service

sudo chmod 644 /lib/systemd/system/power.service

Enable the service

sudo systemctl daemon-reload

sudo systemctl enable power.service

This starts /home/bernard/git/timelapse/power.py on boot up.

Useful functions to test the service:

sudo systemctl start power

sudo systemctl stop power

sudo systemctl restart power

sudo systemctl status power

sudo systemctl disable power

Display last lines of the journal

sudo journalctl -n

Display and continuously print the latest journal entries

sudo journalctl -f

Power budget:

Note: the 2GB version of the Pi5 has a tested current of less than 1A when running with lite OS, though possibly with a peak current higher than this on startup.

Assume on-time of 20 mins, energy used by Pi:

5V * 1A * 0.33h  = 1.7 watt hours (Wh)

Assuming 0.05 Watt for standby during rest of day
0.05W * 24h = 1.2 Wh.  (ignoring 20 mins less)

Total energy required for 24hr = 3.0 Wh

Waveshare power management unit, has 3x18650 Li-ion, and can give 3A output - so the possible higher startup current of the Pi is covered.

Batteries are rated 3.7V, 2500mAh

Max battery energy capacity 3 x 3.7V x 2.5Ah = 27.75 Wh

So fully charged batteries have plenty of capacity.

Assuming 6V 2.0W Solar panel available from PiHut.

Assume UK weather only gets 1W, then after four hours of daylight:

  1.0(W) x 4(h) = 4.0 Wh

So should get the 3Wh energy required per 24hr.

However after further consideration: UK winter sun may produce less than 1W. This solar panel is advertised as 6V. If panel output drops below 6V, then the management unit may fail to work as it is advertised for an input of 6V and above. So decided to get two 6V solar panels and wire them in series to get a nominal 12V, together with the increased wattage output.

In the off state (but retaining power to the board) power can be minimised with:

 $ sudo -E rpi-eeprom-config --edit

    and edit the following line

    POWER_OFF_ON_HALT=1

The meter shows no current on power down (which can't be right since there's a red LED lit like the eye of Sauron), I'll guess 0.01 of an Amp, so power is 5v x 0.01a = 0.05w

Estimating power requirements. Raspberry Pi 5, 2G version, with passive heatsink. Testing the usb-c line gives around 0.5 Amp on powered up.